The present invention relates to the field of modulators and switches for electromagnetic energy propagating in waveguides. More specifically, the present invention relates to modulators and switches for electromagnetic energy of arbitrary polarization propagating in such waveguides.
The present work relates to a wide variety of apparatus operating at many electromagnetic wavelengths. For brevity, the background of the invention is discussed in connection with the field of integrated optics. The use of electromagnetic waves for carrying communications and other signals in modulated form is well known. In recent years, ever more attention has been focused on the potential of carrying advantageously large amounts of information in modulated form on light waves having optical wavelengths in the infrared, visible, and ultraviolet regions of the electromagnetic spectrum. In order to route information from each of many sources to each of many destinations, means of impressing or modulating the information on the light as well as means of switching the light to the appropriate distination are required. It has been proposed that chip-like substrates of crystalline material be provided with waveguides and electrodes for accomplishing such functions.
In one form of integrated optics switch and modulator, a pair of waveguides or refractive index greater than the surrounding substrate are provided in close parallel relationship to one another with electrodes provided thereon. Unfortunately, in many substances such as lithium niobate (LiNbO.sub.3) and lithium tantalate (LiTaO.sub.3) the modulators and switches so formed have proven to be polarization sensitive. For example, when light having a direction of polarization perpendicular to the substrate plane can be substantially modulated or switched, light with a polarization parallel to the substrate plane is simultaneously disadvantageously unaffected or relatively unaffected.
Accordingly, it is an object of the present invention to extend the capabilities of directional coupler electromagnetic modulator/switches so as to be able to modulate and switch electromagnetic radiation regardless of its polarization makeup.
Also, it is an object of the present invention to provided integrated optics modulators and switches which are able to operate on light of arbitrary polarization.
In addition, it is an object of the present invention to permit considerably relaxed fabricational tolerances in the manufacture of miniature electromagnetic, including optical, modulators and switches by permitting electrical tuning adjustments so that the switching of both polarizations of electromagnetic energy is substantially complete.
It is a further object of the invention to provide electromagnetic modulators and switches having waveguides formed in crystalline material such as LiNbO.sub.3 and LiTaO.sub.3 in which the electrooptic sensitivity of the substance is not substantially degraded by comparison with prior art modulators.
It is still further object of the present invention to provide integrated optics modulators and switches in crystalline waveguides such as LiNbO.sub.3 and LiTaO.sub.3 in which the electrooptic sensitivity of the substance is substantially equal in magnitude to its r.sub.33 coefficient for not one, but both polarization modes.
It is even a further object of the invention to provide electromagnetic modulators and switches in which this dual polarization advantage is provided by a structure utilizing sequential positive and negative wavenumber changes for substantially increased bandwith and/or decreased crosstalk and thus, essentially complete switching.